Fusing agent including a metal bis(dithiolene) complex

ABSTRACT

An example of a fusing agent includes a metal bis(dithiolene) complex, a thiol surfactant, a polar aprotic solvent, and a balance of water. In an example of a method of making the fusing agent, the metal bis(dithiolene) complex is exposed to an aqueous solution including a reducing agent and a thiol surfactant to form a reduced metal bis(dithiolene) complex and to dissolve the reduced metal bis(dithiolene) complex in the aqueous solution. The aqueous solution is incorporated into a vehicle including a water soluble organic solvent and an additive selected from the group consisting of an emulsifier, a surface tension reduction agent, a wetting agent, a scale inhibitor, an anti-deceleration agent, a chelating agent, an antimicrobial agent, and a combination thereof. The fusing agent may be utilized in a three-dimensional printing method and/or incorporated into a three-dimensional printing system.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process usedto make three-dimensional solid parts from a digital model. 3D printingis often used in rapid product prototyping, mold generation, mold mastergeneration, and short run manufacturing. Some 3D printing techniques areconsidered additive processes because they involve the application ofsuccessive layers of material. This is unlike traditional machiningprocesses, which often rely upon the removal of material to create thefinal part. 3D printing often requires curing or fusing of the buildingmaterial, which for some materials may be accomplished usingheat-assisted extrusion, melting, or sintering, and for other materialsmay be accomplished using digital light projection technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a simplified isometric and schematic view of an example of a3D printing system disclosed herein;

FIGS. 2A through 2D are schematic and partially cross-sectional viewsdepicting the formation of a 3D part using examples of a 3D printingmethod disclosed herein;

FIG. 3 is a graph depicting absorbance (y-axis) versus wavelength (nm,x-axis) of two comparative fusing agents and an example of the fusingagent disclosed herein;

FIGS. 4A and 4B are black and white representations of originallycolored photographic images of example 3D printed parts, formed withexamples of the fusing agent disclosed herein; and

FIG. 5 is a flow diagram illustrating an example of a method of makingan example of the fusing agent disclosed herein.

DETAILED DESCRIPTION

Examples of the three-dimensional (3D) printing method and the 3Dprinting system disclosed herein utilize Multi Jet Fusion (MJF). DuringMJF, an entire layer of a build material (also referred to as buildmaterial particles) is exposed to radiation, but a selected region (insome instances less than the entire layer) of the build material isfused and hardened to become a layer of a 3D part. A fusing agent isselectively deposited in contact with the selected region of the buildmaterial. The fusing agent(s) is capable of penetrating into the layerof the build material and spreading onto the exterior surface of thebuild material. This fusing agent is capable of absorbing radiation andconverting the absorbed radiation to thermal energy, which in turn meltsor sinters the build material that is in contact with the fusing agent.This causes the build material to fuse, bind, cure, etc. to form thelayer of the 3D part.

As used herein, the terms “3D printed part,” “3D part,” or “part” may bea completed 3D printed part or a layer of a 3D printed part.

Some fusing agents used in MJF tend to have significant absorption(e.g., 80%) in the visible region (400 nm-780 nm). This absorptiongenerates heat suitable for fusing during 3D printing, which leads to 3Dparts having mechanical integrity and relatively uniform mechanicalproperties (e.g., strength, elongation at break, etc.). This absorption,however, results in strongly colored, e.g., black, 3D parts. in someinstances, it may not be desirable to generate strongly colored parts.Rather, it may be desirable to generate a part that is white, off-white,or some color other than black.

Examples of the fusing agent disclosed herein, which may be utilized inexamples of the method and system disclosed herein, contain a metalbis(dithiolene) complex, which has absorption at wavelengths rangingfrom 600 nm to 1600 nm. The metal bis(dithiolene) complex, and thefusing agent including the complex, is capable of absorbing at least 80%of radiation having wavelengths ranging from 600 nm to 1600 nm.Moreover, the absorption maximum of the metal bis(dithiolene) complexmay undergo a bathochromic shift (e.g., further into the near-infraredregion toward the medium infrared region) or a hypsochromic shift (e.g.,in the near-infrared region toward the visible region) depending uponthe chemistry of the complex and/or fusing agent. As examples, the shiftmay depend upon a polar aprotic solvent present in the fusing agentand/or upon the nature of the functional group(s) attached to thecomplex. Like the visible region absorbing fusing agents, the absorptionof the fusing agents including the metal bis(dithiolene) complexgenerates heat suitable for fusing polymeric or polymeric compositebuild material in contact therewith during 3D printing, which leads to3D parts having mechanical integrity and relatively uniform mechanicalproperties (e.g., strength, elongation at break, etc.).

It has been found that a combination of a polar aprotic solvent and athiol surfactant renders the metal bis(dithiolene) complex i) moresoluble in the polar aprotic solvent and ii) readily reducible at roomtemperature (e.g., from about 18° C. to about 25° C.). As such, aninitial reduction of the metal bis(dithiolene) complex may be initiatedprior to fusing (e.g., during fusing agent formulation), which resultsin the complex changing color. It is to be understood that this changein color is not a loss of color (i.e., is not discoloration as definedherein), and the initially reduced complex still readily absorbs theapplied electromagnetic radiation, in the examples disclosed herein,further reduction of the metal bis(dithiolene) complex may take placeduring and/or after fusing. While not being bound to any theory, it isbelieved that the further reduction of the metal bis(dithiolene) complexmay be due, at least in part, to the heat generated during fusing and/oron a build platform after fusing, the electromagnetic radiation usedduring fusing, the components of the fusing agent, the polymeric orpolymeric composite build material, or a combination thereof. As thecomplex reduces, it may change color and ultimately undergodiscoloration (i.e., become at least substantially colorless). By “atleast substantially colorless,” it is meant that the original color ofthe complex changes or fades to a point that the formed part exhibits acolor of the build material, a color of a colorant present in the fusingagent, or a color of a colorant subsequently applied to the buildmaterial. Thus, the fusing agent, containing the metal bis(dithiolene)complex, may be used to print white 3D parts, off-white 3D parts, orcolored 3D parts.

The polar aprotic solvent may be selected to at least partially dissolvethe metal bis(dithiolene) complex and to react with the complex byreducing it (e.g., via an electron transfer reaction). The reductionreaction may cause a shift in the absorption maximum of the metalbis(dithiolene) complex. In some instances, the shift in the absorptionmaximum of the complex may enable the complex to harvest energy from theelectromagnetic radiation applied during 3D printing. For example, theenergy from the electromagnetic radiation may be harvested when theabsorption maximum wavelength of the complex matches that of the sourceof radiation. As such, it may be desirable to utilize a complex andpolar aprotic solvent combination that will shift the absorption maximumof the complex to the wavelength or within the wavelength range of thesource of radiation. The absorbed radiation and harvested energy mayfuse the portion of the polymeric or polymeric composite build materialin contact with the fusing agent, and may initiate or furtherdiscoloration of the complex, even after the application of theradiation ceases.

The thiol surfactant may be included in the fusing agent to stabilizethe metal bis(dithiolene) complex. In particular, the thiol surfactantmay render the complex more soluble in a vehicle of the fusing agent,thus reducing its tendency to precipitate out of the vehicle.Stabilizing the metal bis(dithiolene) complex with the thiol surfactantmay also facilitate the reduction of the metal bis(dithiolene) complexby the polar aprotic solvent (i.e., may enable the reduction to occur atroom temperature and within a few seconds) and/or improve thejettability of the fusing agent.

The fusing agent disclosed herein generally includes a liquid vehicleand the metal bis(dithiolene) complex. The metal bis(dithiolene) complexallows the fusing agent to absorb radiation at wavelengths ranging from600 nm to 1600 nm, which enables the fusing agent to convert enoughradiation to thermal energy so that the polymeric or polymeric compositebuild material particles in contact with the fusing agent fuse.

Examples of the metal bis(dithiolene) complex may have a general formula

Examples of M include nickel, zinc, platinum, palladium, and molybdenum.Examples of each of W, X, Y, and Z include a hydrogen (H), a phenylgroup (Ph), a phenyl group bonded to an R group (i.e., PhR), wherein Ris C_(n)H_(2n+1), or OC_(n)H_(2n+1), or N(CH₃)₂, and a sulfur bonded toan R group (i.e., SR), wherein R is C_(n)H_(2n+1), or OC_(n)H_(2n+1), orN(CH₃)₂. In these examples, n may be greater than or equal to 2 and lessthan or equal to 12 (i.e., 2≤n≤12). When the metal bis(dithiolene)complex has the general formula I, the strong NIR absorption of themetal bis(dithiolene) complex may be the result of the electrondelocalization about the dithiolene ring and the interaction of thedelocalized electrons with the empty d-orbitals of the metal center.

The amount of the metal bis(dithiolene) complex in the fusing agent mayrange from about 1 wt % to about 3 wt % based on the total wt % of thefusing agent. In an example, the amount of the metal bis(dithiolene)complex present in the fusing agent is about 1 wt % based on the totalwt % of the fusing agent. It is believed that these metalbis(dithiolene) complex loadings provide a balance between the fusingagent having jetting reliability and electromagnetic radiationabsorbance efficiency.

As mentioned above, the polar aprotic solvent may be included in thefusing agent to at least partially dissolve the metal bis(dithiolene)complex and to shift the absorption of the metal bis(dithiolene)complex. In some instances, the shift is further into the near-infrared(NIR) region (e.g., shifting from an absorption maximum of about 850 nmwhen the metal bis(dithiolene) complex is not reduced to an absorptionmaximum of about 940 nm when metal bis(dithiolene) complex is reduced(e.g., to its monoanionic form or to its dianionic form)). The polaraprotic solvent may shift the absorption maximum of the metalbis(dithiolene) complex by reducing the metal bis(dithiolene) complex toits monoanionic form or to its dianionic form according to equation II:

The reduction of the metal bis(dithiolene) complex to its monoanionicform or to its dianionic form (left side of equation II) may shift theabsorption maximum of the metal bis(dithiolene) complex up to about 100nm, depending, in part, upon the solvent that is used. For example,1-methyl-2-pyrrolidone may shift the absorption maximum to about 925 nm,and a 94 nm shift in the absorption maximum may be observed whenswitching from toluene to DMF, When the metal bis(dithiolene) complex isreduced to its monoanionic form or to its dianionic form, the color ofthe metal bis(dithiolene) complex may change. For example, the initialreduction of a nickel bis(dithiolene) complex may result in the colorchanging from green to reddish brown. Other color changes may beobserved with different metals in the complex. As noted above, the colorchanged complex can still absorb infrared radiation, and becomes atleast substantially colorless during the application of theelectromagnetic radiation.

In some examples, the polar aprotic solvent is a polar aprotic solventcontaining a tert-amide. In other examples, the polar aprotic solvent isa polar aprotic solvent containing a sec-amine or a tert-amine. In stillother examples, the polar aprotic solvent is an organosulfur, a ketone,or an ether. Some specific examples of the polar aprotic solvent include1-methyl-2-pyrrolidone (1M2P), 2-pyrrolidone,1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide (DMF), dimethylsulfoxide (DMSO), and combinations thereof.

The polar aprotic solvent is present in the fusing agent in an amountsufficient to reduce the metal bis(dithiolene) complex to itsmonoanionic form or to its dianionic form. In an example, the amount ofthe polar aprotic solvent in the fusing agent may range from about 5 wt% to about 50 wt % based on the total wt % of the fusing agent. Inanother example, the amount of the polar aprotic solvent present in thefusing agent is about 40 wt % based on the total wt % of the fusingagent. In still another example, the amount of the polar aprotic solventpresent in the fusing agent is about 50 wt % based on the total wt % ofthe fusing agent.

As also mentioned above, the thiol surfactant may be included in thefusing agent to stabilize the metal bis(dithiolene) complex. The thiolsurfactant may facilitate the reduction of the metal bis(dithiolene)complex by the polar aprotic solvent. More specifically, the thiolsurfactant may render the complex readily reducible and thus moresoluble in the polar aprotic solvent. Without the thiol surfactant, thereduction of the metal bis(dithiolene) complex to its monoanionic formor to its dianionic form may require the mixture of the neutral,non-reduced metal bis(dithiolene) complex and the polar aprotic solventto be heated to an elevated temperature (e.g., a temperature rangingfrom about 50° C. to about 200° C.) for an extended time period (e.g., atime period ranging from about 5 hours to about 48 hours). When thethiol surfactant is included in the mixture of the metal bis(dithiolene)complex and the polar aprotic solvent, the reduction of the metalbis(dithiolene) complex to its monoanionic form or to its dianionic formmay be accomplished at room temperature (e.g., from about 18° C. toabout 25° C.) and within a few seconds (e.g., less than 10 seconds).

The thiol surfactant may also improve the jettability of the fusingagent by stabilizing the metal bis(dithiolene) complex. Without thethiol surfactant, the metal bis(dithiolene) complex may precipitate outof solution when water or a liquid vehicle is added. When the thiolsurfactant is included in the mixture of the metal bis(dithiolene)complex and the polar aprotic solvent, the reduced metal bis(dithiolene)complex can be easily formulated into (i.e., dissolved or dispersedrather than precipitated out of) a liquid vehicle.

An example of the thiol surfactant is dodecanethiol, 1-undecanethiol,2-ethyihexanethiol, 1-octanethiol, 1-tetradecanethiol, and combinationsthereof.

The thiol surfactant is present in the fusing agent in an amountsufficient to stabilize the metal bis(dithiolene) complex. In anexample, the amount of the thiol surfactant in the fusing agent mayrange from about 1 wt % to about 5 wt % based on the total wt % of thefusing agent.

As used herein, “FA vehicle” may refer to the liquid fluid in which themetal bis(dithiolene) complex is placed to form the fusing agent. A widevariety of FA vehicles may be used with the fusing agent, system, andmethod of the present disclosure. The FA vehicle may include water,alone or in combination with a mixture of a variety of additionalcomponents. Examples of these additional components may include watersoluble organic solvent(s), wetting agent(s), surface tension reductionagent(s), emulsifier(s), scale inhibitor(s), anti-deceleration agent(s),chelating agent(s), and/or antimicrobial agent(s).

One example FA vehicle includes water, the polar aprotic solvent, andthe thiol surfactant. Another example FA vehicle consists of water, thepolar aprotic solvent, and the thiol surfactant (without any othercomponents).

The water in the FA vehicle may prevent (further) reduction of the metalbis(dithiolene) complex until the water is driven off as a result of thebuild material platform temperature and/or the temperature achievedduring radiation exposure. After the water is driven off, the metalbis(dithiolene) complex is capable of being further reduced and becomingcolorless/discolored, which enables the 3D part to exhibit a color ofthe build material (e.g., white or off-white) or to exhibit a color of acolorant present in the fusing agent.

The aqueous nature of the fusing agent enables the fusing agent topenetrate, at least partially, into the layer of the polymeric orpolymeric composite build material particles. The build materialparticles may be hydrophobic, and the presence of the wetting agent(s)in the fusing agent may assist in obtaining a particular wettingbehavior.

Examples of suitable wetting agents include non-ionic surfactants. Somespecific examples include a self-emulsifiable, non-ionic wetting agentbased on acetylenic diol chemistry (e.g., SURFYNOL® SEF from AirProducts and Chemicals, Inc.), a non-ionic fluorosurfactant (e.g.,CAPSTONE® fluorosurfactants from DuPont, previously known as ZONYL FSO),and combinations thereof. In other examples, the wetting agent is anethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL®CT-111 from Air Products and Chemical Inc.) or an ethoxylated wettingagent and molecular defoamer (e.g., SURFYNOL@ 420 from Air Products andChemical Inc.). Still other suitable wetting agents include non-ionicwetting agents and molecular defoamers (e.g., SURFYNOL® 104E from AirProducts and Chemical Inc.) or water-soluble, non-ionic surfactants(e.g., TERGITOL™ TMN-6, TERGITOL™ 15S7, and TERGITOL™ 15S9 from The DowChemical Company). In some examples, an anionic surfactant may be usedin combination with the non-ionic surfactant. In some examples, it maybe desirable to utilize a wetting agent having a hydrophilic-lipophilicbalance (HLB) less than 10.

The wetting agent(s) may be present in the fusing agent in an amountranging from about 0.1 wt % to about 4 wt % of the total wt % of thefusing agent. In an example, the amount of the wetting agent(s) presentin the fusing agent is about 0.1 wt % (based on the total wt % of thefusing agent). In another example, the amount of the wetting agent(s)present in the fusing agent is about 0.04 wt % (based on the total wt %of the fusing agent).

The FA vehicle may also include surface tension reduction agent(s). Anyof the previously mentioned wetting agents/surfactants may be used toreduce the surface tension. As an example, the surface tension reductionagent may be the self-emulsifiable, non-ionic wetting agent based onacetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products andChemicals, Inc.).

The surface tension reduction agent(s) may be present in the fusingagent in an amount ranging from about 0.1 wt % to about 4 wt % of thetotal wt % of the fusing agent. In an example, the amount of the surfacetension reduction agent(s) present in the fusing agent is about 1.5 wt %(based on the total wt % of the fusing agent). In another example, theamount of the surface tension reduction agent(s) present in the fusingagent is about 0.6 wt % (based on the total wt % of the fusing agent).

When a surfactant is both a wetting agent and a surface tensionreduction agent, any of the ranges presented herein for the wettingagent and the surface tension reduction agent may be used for thesurfactant.

The FA vehicle may also include water soluble organic solvent(s). Insome examples, the water soluble organic solvent(s) may be the same typeof solvent as the polar aprotic solvent. In these examples, the watersoluble organic solvent(s) may be 1-methyl-2-pyrrolidone (1M2P),2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide(DMF), dimethyl sulfoxide (DMSO), or a combination thereof. In otherexamples, the water soluble organic solvent(s) may be different than thepolar aprotic solvent. For example, two different polar aprotic solventsmay be selected. For another example, the water soluble organicsolvent(s) may be 1,5-pentanediol, triethylene glycol, tetraethyleneglycol, 2-methyl-1,3-propanediol, 1,6-hexanediol, tripropylene glycolmethyl ether, or a combination thereof.

The water soluble organic solvent(s) may be present in the fusing agentin an amount ranging from about 2 wt % to about 80 wt % of the total wt% of the fusing agent. In an example, the amount of the water solubleorganic solvent(s) present in the fusing agent is about 40 wt % (basedon the total wt % of the fusing agent). In another example, the amountof the water soluble organic solvent(s) present in the fusing agent isabout 16 wt % (based on the total wt % of the fusing agent).

The FA vehicle may also include emulsifier(s). Examples of suitableemulsifiers include oleth-3-phosphate (commercially available asCRODAFOS™ O3A or CRODAFOS™ N-3 acid) or dextran 500k. Other suitableexamples of the emulsifiers include CRODAFOS™ HCE (phosphate-ester fromCroda Int.), CRODAFOS® N10 (oleth-10-phosphate from Croda Int.), etc.

The emulsifier(s) may be present in the fusing agent in an amountranging from about 0.1 wt % to about 2 wt % of the total wt % of thefusing agent. In an example, the amount of the emulsifier(s) present inthe fusing agent is about 1 wt % (based on the total wt % of the fusingagent). In another example, the amount of the emulsifier(s) present inthe fusing agent is about 0.4 wt % (based on the total wt % of thefusing agent).

The fusing agent may include scale inhibitor(s) or anti-decelerationagent(s). One suitable scale inhibitor/anti-deceleration agent is analkyldiphenyloxide disulfonate (e.g., DOWFAX™ 8390 and DOWFAX™ 2A1 fromThe Dow Chemical Company).

The scale inhibitor(s)/anti-deceleration agent(s) may be present in thefusing agent in an amount ranging from about 0.05 wt % to about 5 wt %of the total wt % of the fusing agent. In an example, the scaleinhibitor(s)/anti-deceleration agent(s) is/are present in the fusingagent in an amount of about 0.25 wt % (based on the total wt % of thefusing agent). In another example, the scaleinhibitor(s)/anti-deceleration agent(s) is/are present in the fusingagent in an amount of about 0.1 wt % (based on the total wt % of thefusing agent).

The fusing agent may also include chelating agent(s). The chelatingagent may be included to eliminate the deleterious effects of heavymetal impurities. Examples of suitable chelating agents include disodiumethylenediaminetetraacetic acid (EDTA-Na), ethylene diamine tetra aceticacid (EDTA), and methylglycinediacetic acid (e.g., TRILON® M from BASFCorp.).

Whether a single chelating agent is used or a combination of chelatingagents is used, the total amount of chelating agent(s) in the fusingagent may range from 0 wt % to about 2 wt % based on the total wt % ofthe fusing agent. In an example, the chelating agent is present in thefusing agent in an amount of about 0.08 wt % (based on the total wt % ofthe fusing agent). In another example, the chelating agent is present inthe fusing agent in an amount of about 0.032 wt % (based on the total wt% of the fusing agent).

The FA vehicle may also include antimicrobial agent(s). Suitableantimicrobial agents include biocides and fungicides. Exampleantimicrobial agents may include the NUOSEPT® (Ashland Inc.), UCARCIDE™or KORDEK™ (Dow Chemical Co.), and PROXELr (Arch Chemicals) series,ACTICIDE®@ M20 (Thor), and combinations thereof.

In an example, the fusing agent may include a total amount ofantimicrobial agents that ranges from about 0.1 wt % to about 0.35 wt %.In an example, the antimicrobial agent is a biocide and is present inthe fusing agent in an amount of about 0.32 wt % (based on the total wt% of the fusing agent). In another example, the antimicrobial agent is abiocide and is present in the fusing agent in an amount of about 0.128wt % (based on the total wt % of the fusing agent).

The balance of the fusing agent is water. As an example, deionized watermay be used.

In an example, the fusing agent includes from about 1 wt % to about 3 wt% of the metal bis(dithiolene) complex, from about 1 wt % to about 5 wt% of the thiol surfactant, from about 5 wt % to about 50 wt % of thepolar aprotic solvent, and a balance of water (based on the total wt %of the fusing agent).

In some examples the fusing agent may include a colorant in addition tothe metal bis(dithiolene) complex. While the metal bis(dithiolene)complex functions as an electromagnetic radiation absorber and becomescolorless after fusing the build material, the additional colorant mayimpart color to the fusing agent and the resulting 3D part. The amountof the colorant that may be present in the fusing agent ranges fromabout 1 wt % to about 10 wt % based on the total wt % of the fusingagent. The colorant may be a pigment and/or dye having any suitablecolor. Examples of the colors include cyan, magenta, yellow, etc.Examples of colorants include dyes, such as Acid Yellow 23 (AY 23), AcidYellow 17 (AY 17), Acid Red 52 (AR 52), Acid Red 289 (AR 289), ReactiveRed 180 (RR 180), Direct Blue 199 (DB 199), or pigments, such as PigmentBlue 15:3 (PB 15:3), Pigment Red 122 (PR 122), Pigment Yellow 155 (PY155), and Pigment Yellow 74 (PY 74).

In some other examples, the fusing agent excludes a colorant other thanthe metal bis(dithiolene) complex. It may be desirable to exclude thecolorant from the fusing agent when the 3D part to be created is to bethe color of the polymeric or polymeric composite build material (e.g.,white or off-white) or when a colored ink will be applied to the 3Dpart.

Also disclosed herein is a method of making the fusing agent. An exampleof this method 200 is shown in FIG. 5. As shown at reference numeral 202of FIG. 5, the fusing agent may be prepared by exposing a metalbis(dithiolene) complex to a solution including a reducing agent and athiol surfactant, thereby forming a reduced metal bis(dithiolene)complex and dissolving the reduced metal bis(dithiolene) complex in thesolution. As shown at reference numeral 204 of FIG. 5, an example of themethod 200 further includes incorporating the solution into a vehicleincluding a water soluble organic solvent and an additive selected fromthe group consisting of an emulsifier, a surface tension reductionagent, a wetting agent, a scale inhibitor, an anti-deceleration agent, achelating agent, an antimicrobial agent, and a combination thereof.

As previously mentioned, the solution to which the metal bis(dithiolene)complex is exposed includes at least the reducing agent and the thiolsurfactant, In some instances, this solution may also include water. Themetal bis(dithiolene) complex may be reduced to its monoanionic form orto its dianionic form by the reducing agent in the solution. The reducedmetal bis(dithiolene) complex may then dissolve in the solution.

In some examples, the metal bis(dithiolene) complex is exposed to thesolution at room temperature (e.g., a temperature ranging from about 18°C. to about 25° C. The metal bis(dithiolene) complex may be reduced anddissolved in the solution within few seconds (e.g., less than 10seconds).

In some examples, the reducing agent is the polar aprotic solvent thatis included in the fusing agent. In these examples, the reducing agentmay be 1-methyl-2-pyrrolidone (1M2P), 2-pyrrolidone,1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide (DMF), dimethylsulfoxide (DMSO), or a combination thereof. In other examples, thereducing agent is different than the polar aprotic solvent that isincluded in the fusing agent. When the reducing agent is different thanthe polar aprotic solvent in the fusing agent, the reducing agent may beselected from reducing agents that are capable of reducing the metalbis(dithiolene) complex to its monoanionic form or to its dianionic formand that are compatible with the FA vehicle (i.e., able to be formulatedinto the FA vehicle).

As mentioned above, examples of the metal bis(dithiolene) complex havethe general formula I:

Examples of M include nickel, zinc, platinum, palladium, and molybdenum.Examples of each of W, X, Y, and Z include a hydrogen, a phenyl group, aphenyl group bonded to C_(n)H_(2n+1), or OC_(n)H_(2n+1), or N(CH₃)₂, anda sulfur bonded to C H_(2n+1), or OC_(n)H_(2n+1), or N(CH₃)₂. In theseexamples, n may be greater than or equal to 2 and less than or equal to12.

As also mentioned above, the thiol surfactant may be dodecanethiol,1-undecanethiol, 2-ethylhexanethiol, 1-octanethiol, 1-tetradecanethiol,or the like.

After the metal bis(dithiolene) complex is reduced and dissolved in thesolution, the solution may be incorporated into the FA vehicle(reference numeral 204 of FIG. 5). As mentioned above, the FA vehiclemay include water, a water soluble organic solvent, and an additiveselected from the group consisting of an emulsifier, a surface tensionreduction agent, a wetting agent, a scale inhibitor, ananti-deceleration agent, a chelating agent, an antimicrobial agent, anda combination thereof. The water soluble organic solvent and theadditive may be any of examples and may be included in any of theamounts described above.

Referring now to FIG. 1, an example of a 3D printing system 10 isschematically depicted. It is to be understood that the 3D printingsystem 10 may include additional components and that some of thecomponents described herein may be removed and/or modified. Furthermore,components of the 3D printing system 10 depicted in FIG. 1 may not bedrawn to scale and thus, the 3D printing system 10 may have a differentsize and/or configuration other than as shown therein.

The printing system 10 includes a build area platform 12, a buildmaterial supply 14 containing polymeric or polymeric composite buildmaterial particles 16, and a build material distributor 18.

The build area platform 12 receives the polymeric or polymeric compositebuild material 16 from the build material supply 14. The build areaplatform 12 may be integrated with the printing system 10 or may be acomponent that is separately insertable into the printing system 10. Forexample, the build area platform 12 may be a module that is availableseparately from the printing system 10. The build material platform 12that is shown is also one example, and could be replaced with anothersupport member, such as a platen, a fabrication/print bed, a glassplate, or another build surface.

The build area platform 12 may be moved in a direction as denoted by thearrow 20, e.g., along the z-axis, so that polymeric or polymericcomposite build material 16 may be delivered to the platform 12 or to apreviously formed layer of the 3D part. In an example, when thepolymeric or polymeric composite build material particles 16 are to bedelivered, the build area platform 12 may be programmed to advance(e.g., downward) enough so that the build material distributor 18 canpush the polymeric or polymeric composite build material particles 16onto the platform 12 to form a substantially uniform layer of thepolymeric or polymeric composite build material 16 thereon (see, e.g.,FIGS. 2A and 2B). The build area platform 12 may also be returned to itsoriginal position, for example, when a new part is to be built.

The build material supply 14 may be a container, bed, or other surfacethat is to position the polymeric or polymeric composite build materialparticles 16 between the build material distributor 18 and the buildarea platform 12. In some examples, the build material supply 14 mayinclude a surface upon which the polymeric or polymeric composite buildmaterial particles 16 may be supplied, for instance, from a buildmaterial source (not shown) located above the build material supply 14.Examples of the build material source may include a hopper, an augerconveyer, or the like. Additionally, or alternatively, the buildmaterial supply 14 may include a mechanism (e.g., a delivery piston) toprovide, e.g., move, the polymeric or polymeric composite build materialparticles 16 from a storage location to a position to be spread onto thebuild area platform 12 or onto a previously formed layer of the 3D part.

The build material distributor 18 may be moved in a direction as denotedby the arrow 22, e.g., along the y-axis, over the build material supply14 and across the build area platform 12 to spread a layer of thepolymeric or polymeric composite build material 16 over the build areaplatform 12. The build material distributor 18 may also be returned to aposition adjacent to the build material supply 14 following thespreading of the polymeric or polymeric composite build materialparticles 16. The build material distributor 18 may be a blade (e.g., adoctor blade), a roller, a combination of a roller and a blade, and/orany other device capable of spreading the polymeric or polymericcomposite build material 16 over the build area platform 12. Forinstance, the build material distributor 18 may be a counter-rotatingroller.

The polymeric or polymeric composite build material particles 16 may bea polymeric build material or a polymeric composite build material. Asused herein, the term “polymeric build material” may refer tocrystalline or semi-crystalline polymer particles. As used herein, theterm “polymeric composite build material” may refer or compositeparticles made up of polymer and ceramic. Any of the polymeric orpolymeric composite build material particles 16 may be in powder form.

Examples of semi-crystalline polymers include semi-crystallinethermoplastic materials with a wide processing window of greater than 5°C. (i.e., the temperature range between the melting point and there-crystallization temperature). Some specific examples of thesemi-crystalline thermoplastic materials include polyamides (PAs) (e.g.,PA 11/nylon 11, PA 12/nylon 12, PA 6/nylon 6, PA 8/nylon 8, PA 9/nylon9, PA 66/nylon 66, PA 612/nylon 612, PA 812/nylon 812, PA 912/nylon 912,etc.). Other examples of crystalline or semi-crystalline polymerssuitable for use as the build material particles 16 includepolyethylene, polypropylene, and polyoxomethylene (i.e., polyacetals).Still other examples of suitable build material particles 16 includepolystyrene, polycarbonate, polyester, polyurethanes, other engineeringplastics, and blends of any two or more of the polymers listed herein.

Any of the previously listed crystalline or semi-crystalline polymerparticles may be combined with ceramic particles to form the polymericcomposite build material particles 16. Examples of suitable ceramicparticles include metal oxides, inorganic glasses, carbides, nitrides,and borides. Some specific examples include alumina (Al₂O₃), glass,silicon mononitride (SiN), silicon dioxide (SiOC₂), zirconia (ZrO₂),titanium dioxide (TiO₂), or combinations thereof. The amount of ceramicparticles that may be combined with the crystalline or semi-crystallinepolymer particles may depend on the materials used and the 3D part to beformed. In one example, the ceramic particles may be present in anamount ranging from about 1 wt % to about 20 wt % based on the total wt% of the polymeric composite build material particles 16.

The polymeric or polymeric composite build material particles 16 mayhave a melting point or softening point ranging from about 50° C. toabout 400° C. As an example, the build material particles 16 may be apolyamide having a melting point of 180° C.

The polymeric or polymeric composite build material particles 16 may bemade up of similarly sized particles or differently sized particles. Theterm “size”, as used herein with regard to the polymeric or polymericcomposite build material particles 16, refers to the diameter of aspherical particle, or the average diameter of a non-spherical particle(i.e., the average of multiple diameters across the particle), or thevolume-weighted mean diameter of a particle distribution. In an example,the average size of the polymeric or polymeric composite build materialparticles 16 ranges from 5 μm to about 200 μm.

It is to be understood that the polymeric or polymeric composite buildmaterial 16 may include, in addition to polymeric or polymeric compositeparticles, a charging agent, a flow aid, or combinations thereof.

Charging agent(s) may be added to suppress tribo-charging. Examples ofsuitable charging agent(s) include aliphatic amines (which may beethoxylated), aliphatic amides, quaternary ammonium salts (e.g.,behentrimonium chloride or cocamidopropyl betaine), esters of phosphoricacid, polyethylene glycolesters, or polyols. Some suitable commerciallyavailable charging agents include HOSTASTAT® FA 38 (natural basedethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), andHOSTASTAT® HS 1 (alkane sulfonate), each of which is available fromClariant Int. Ltd.). In an example, the charging agent is added in anamount ranging from greater than 0 wt % to less than 5 wt % based uponthe total wt % of the polymeric or polymeric composite build material16.

Flow aid(s) may be added to improve the coating flowability of thepolymeric or polymeric composite build material 16. Flow aid(s) may beparticularly beneficial when the particles of the polymeric or polymericcomposite build material 16 are less than 25 μm in size. The flow aidimproves the flowability of the polymeric or polymeric composite buildmaterial 16 by reducing the friction, the lateral drag, and thetribocharge buildup (by increasing the particle conductivity). Examplesof suitable flow aids include tricalcium phosphate (E341), powderedcellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate(E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536),calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate(E550), silicon dioxide (E551), calcium silicate (E552), magnesiumtrisilicate (E553a), talcum powder (E553b), sodium aluminosilicate(E554), potassium aluminum silicate (E555), calcium aluminosilicate(E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570),or polydimethylsiloxane (E900). In an example, the flow aid is added inan amount ranging from greater than 0 wt % to less than 5 wt % basedupon the total wt % of the polymeric or polymeric composite buildmaterial 16.

As shown in FIG. 1, the printing system 10 also includes an applicator24, which may contain the fusing agent 26 disclosed herein.

As mentioned above, the fusing agent 26 may include the metalbis(dithiolene) complex and the FA vehicle. In an example, the fusingagent 26 includes the metal bis(dithiolene) complex, the thiolsurfactant, the polar aprotic solvent, and a balance of water. Inanother example, the fusing agent 26 consists of these components and noother components. In still another example, the fusing agent 26 includesfrom about 1 wt % to about 3 wt % of the metal bis(dithiolene) complex,from about 1 wt % to about 5 wt % of the thiol surfactant, from about 5wt % to about 50 wt % of the polar aprotic solvent, and a balance ofwater (based on the total wt % of the fusing agent 26). As alsomentioned above, in some examples, the fusing agent 26 includes thecolorant. In an example, the fusing agent 26 consists of the metalbis(dithiolene) complex, the thiol surfactant, the polar aproticsolvent, the colorant, and a balance of water. In still other examples,the fusing agent 26 excludes the colorant.

The applicator 24 may be scanned across the build area platform 12 inthe direction indicated by the arrow 28, e.g., along the y-axis. Theapplicator 24 may be, for instance, a thermal inkjet printhead, apiezoelectric printhead, a continuous inkjet printhead, etc., and mayextend a width of the build area platform 12. While the applicator 24 isshown in FIG. 1 as a single applicator, it is to be understood that theapplicator 24 may include multiple applicators that span the width ofthe build area platform 12. Additionally, the applicators 24 may bepositioned in multiple printbars. The applicator 24 may also be scannedalong the x-axis, for instance, in configurations in which theapplicator 24 does not span the width of the build area platform 12 toenable the applicator 24 to deposit the fusing agent 26 over a largearea of a layer of polymeric or polymeric composite build materialparticles 16. The applicator 24 may thus be attached to a moving XYstage or a translational carriage (neither of which is shown) that movesthe applicator 24 adjacent to the build area platform 12 in order todeposit the fusing agent 26 in predetermined areas of a layer of thepolymeric or polymeric composite build material particles 16 that hasbeen formed on the build area platform 12 in accordance with themethod(s) disclosed herein. The applicator 24 may include a plurality ofnozzles (not shown) through which the fusing agent 26 is to be ejected.

The applicator 24 may deliver drops of the fusing agent 26 at aresolution ranging from about 300 dots per inch (DPI) to about 1200 DPI.In other examples, the applicator 24 may deliver drops of the fusingagent 26 at a higher or lower resolution. The drop velocity may rangefrom about 5 m/s to about 24 m/s and the firing frequency may range fromabout 1 kHz to about 100 kHz. In one example, each drop may be in theorder of about 10 picoliters (μl) per drop, although it is contemplatedthat a higher or lower drop size may be used. In some examples,applicator 24 is able to deliver variable size drops of the fusing agent26.

In some examples of the system 10 disclosed herein, another applicator(not shown) may be included that is capable of applying a colored ink tothe 3D part that is formed. This applicator may be similar to or thesame as applicator 24. It may be desirable to include this applicatorand the colored ink when the 3D part is the color of the polymeric orpolymeric composite build material (e.g., white or off-white), and whenit is desirable to apply color to the white or off-white 3D part.

An example of a pigment based colored ink may include from about 1 wt %to about 10 wt % of pigment(s), from about 10 wt % to about 30 wt % ofco-solvent(s), from about 0.5 wt % to about 2 wt % of dispersant(s),from 0.01 wt % to about 1 wt % of anti-kogation agent(s), from about 0.1wt % to about 5 wt % of binder(s), from about 0.05 wt % to about 0.1 wt% biocide(s), and a balance of water. An example of a dye based coloredink may include from about 1 wt % to about 7 wt % of dye(s), from about10 wt % to about 30 wt % of co-solvent(s), from about 0.25 wt % to about2 wt % of dispersant(s), from 0.05 wt % to about 0.1 wt % of chelatingagent(s), from about 0.005 wt % to about 0.2 wt % of buffer(s), fromabout 0.05 wt % to about 0.1 wt % biocide(s), and a balance of water.Some specific examples of suitable colored inks include a set of cyan,magenta, and yellow inks, such as C1893A (cyan), C1984A (magenta), andC1985A (yellow); or C4801A (cyan), C4802A (magenta), and C4803A(yellow); all of which are available from HP Inc. Other commerciallyavailable colored inks include C9384A (printhead HP 72), C9383A(printhead HP 72), C4901A (printhead HP 940), and C4900A (printhead HP940).

Each of the previously described physical elements may be operativelyconnected to a controller 30 of the prnting system 10. The controller 30may control the operations of the build area platform 12, the buildmaterial supply 14, the build material distributor 18, and theapplicator 24. As an example, the controller 30 may control actuators(not shown) to control various operations of the 3D printing system 10components. The controller 30 may be a computing device, asemiconductor-based microprocessor, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), and/or another hardwaredevice, Although not shown, the controller 30 may be connected to the 3Dprinting system 10 components via communication lines.

The controller 30 manipulates and transforms data, which may berepresented as physical (electronic) quantities within the printer'sregisters and memories, in order to control the physical elements tocreate the 3D part. As such, the controller 30 is depicted as being incommunication with a data store 32. The data store 32 may include datapertaining to a 3D part to be printed by the 3D printing system 10. Thedata for the selective delivery of the polymeric or polymeric compositebuild material particles 16, the fusing agent 26, etc. may be derivedfrom a model of the 3D part to be formed. For instance, the data mayinclude the locations on each layer of polymeric or polymer compositebuild material particles 16 that the applicator 24 is to deposit thefusing agent 26. In one example, the controller 30 may use the data tocontrol the applicator 24 to selectively apply the fusing agent 26. Thedata store 32 may also include machine readable instructions (stored ona non-transitory computer readable medium) that are to cause thecontroller 30 to control the amount of polymeric or polymeric compositebuild material particles 16 that is supplied by the build materialsupply 14, the movement of the build area platform 12, the movement ofthe build material distributor 18, the movement of the applicator 24,etc.

As shown in FIG. 1, the printing system 10 may also include a source ofelectromagnetic radiation 34, 34′. In some examples, the source ofelectromagnetic radiation 34, 34′ may be in a fixed position withrespect to the build material platform 12. In other examples, the sourceof electromagnetic radiation 34, 34′ may be positioned to expose thelayer of polymeric or polymeric composite build material particles 16 toelectromagnetic radiation immediately after the fusing agent 26 has beenapplied thereto. In the example shown in FIG. 1, the source ofelectromagnetic radiation 34′ is attached to the side of the applicator24 which allows for patterning and heating in a single pass.

The source of electromagnetic radiation 34, 34′ may emit electromagneticradiation having wavelengths ranging from about 800 nm to about 1 mm. Asone example, the electromagnetic radiation may range from about 800 nmto about 2 μm. As another example, the electromagnetic radiation may beblackbody radiation with a maximum intensity at a wavelength of about1100 nm. The source of electromagnetic radiation 34, 34′ may be infrared(IR) or near-infrared light sources, such as IR or near-IR curing lamps,IR or near-IR light emitting diodes (LED), or lasers with the desirableIR or near-IR electromagnetic wavelengths.

The source of electromagnetic radiation 34, 34′ may be operativelyconnected to a lamp/laser driver, an input/output temperaturecontroller, and temperature sensors, which are collectively shown asradiation system components 36. The radiation system components 36 mayoperate together to control the source of electromagnetic radiation 34,34′. The temperature recipe (e.g., radiation exposure rate) may besubmitted to the input/output temperature controller. During heating,the temperature sensors may sense the temperature of the polymeric orpolymeric composite build material particles 16, and the temperaturemeasurements may be transmitted to the input/output temperaturecontroller. For example, a thermometer associated with the heated areacan provide temperature feedback. The input/output temperaturecontroller may adjust the source of electromagnetic radiation 34, 34′power set points based on any difference between the recipe and thereal-time measurements. These power set points are sent to thelamp/laser drivers, which transmit appropriate lamp/laser voltages tothe source of electromagnetic radiation 34, 34′. This is one example ofthe radiation system components 36, and it is to be understood thatother radiation source control systems may be used. For example, thecontroller 30 may be configured to control the source of electromagneticradiation 34, 34′.

Referring now to FIGS. 2A through 2D, an example of the 3D printingmethod 100 is depicted. This method 100 may be used to form 3D printedparts having mechanical integrity (e.g., having an ultimate tensilestrength ranging from about 40 MPa to about 55 MPa) and being white,off-white, or colored. In other examples, the ultimate tensile strengthof the 3D printed part may range from about 40 MPa to about 51 MPa orfrom about 40 MPa to about 45 MPa.

Prior to execution of the method 100 or as part of the method 100, thecontroller 30 may access data stored in the data store 32 pertaining toa 3D part that is to be printed. The controller 30 may determine thenumber of layers of polymeric or polymeric composite build material 16that are to be formed, and the locations at which the fusing agent 26from the applicator 24 is to be deposited on each of the respectivelayers.

As shown in FIGS. 2A and 2B, the method 100 includes applying thepolymeric or polymeric composite build material 16. In FIG. 2A, thebuild material supply 14 may supply the polymeric or polymeric compositebuild material particles 16 into a position so that they are ready to bespread onto the build area platform 12. In FIG. 2B, the build materialdistributor 18 may spread the supplied polymeric or polymeric compositebuild material particles 16 onto the build area platform 12. Thecontroller 30 may execute control build material supply instructions tocontrol the build material supply 14 to appropriately position thepolymeric or polymeric composite build material particles 16, and mayexecute control spreader instructions to control the build materialdistributor 18 to spread the supplied polymeric or polymeric compositebuild material particles 16 over the build area platform 12 to form alayer 38 of polymeric or polymeric composite build material particles 16thereon. As shown in FIG. 2B, one layer 38 of the polymeric or polymericcomposite build material particles 16 has been applied.

The layer 38 has a substantially uniform thickness across the build areaplatform 12. In an example, the thickness of the layer 38 ranges fromabout 50 μm to about 300 μm, although thinner or thicker layers may alsobe used. For example, the thickness of the layer 38 may range from about20 μm to about 500 μm, or from about 30 μm to about 300 μm. The layerthickness may be about 2× the particle diameter (as shown in FIG. 2B) ata minimum for finer part definition.

Prior to further processing, the layer 38 of the polymeric or polymericcomposite build material particles 16 may be exposed to heating. Heatingmay be performed to pre-heat the polymeric or polymeric composite buildmaterial particles 16, and thus the heating temperature may be below themelting point or softening point of the polymeric or polymeric compositebuild material particles 16. As such, the temperature selected willdepend upon the polymeric or polymeric composite build materialparticles 16 that are used. As examples, the pre-heating temperature maybe from about 5° C. to about 50° C. below the melting point or softeningpoint of the polymeric or polymeric composite build material particles16. In an example, the pre-heating temperature ranges from about 50° C.to about 350° C. In another example, the pre-heating temperature rangesfrom about 150° C. to about 170° C.

Pre-heating the layer 38 of the polymeric or polymeric composite buildmaterial particles 16 may be accomplished using any suitable heat sourcethat exposes all of the polymeric or polymeric composite build materialparticles 16 on the build material surface 12 to the heat. Examples ofthe heat source include a thermal heat source (e.g., a heater (notshown) of the particles 16) or the electromagnetic radiation source 34,34′.

Referring now to FIG. 2C, after the layer 38 is formed, and in someinstances is pre-heated, the fusing agent 26 is selectively applied onat least a portion 40 of the polymeric or polymeric composite buildmaterial 16.

It is to be understood that a single fusing agent 26 may be selectivelyapplied on the portion 40, or multiple fusing agents 26 may beselectively applied on the portion 40. As an example, multiple fusingagents 26 may be used when the colorant is included in at least one ofthe multiple fusing agents 26 to create a multi-colored part.

As illustrated in FIG. 2C, the fusing agent 26 may be dispensed from theapplicator 24. The controller 32 may execute instructions to control theapplicator 24 (e.g., in the directions indicated by the arrow 28) todeposit the fusing agent 26 onto predetermined portion(s) 40 of thepolymeric or polymeric composite build material 16 that are to becomepart of the 3D part. The applicator 24 may be programmed to receivecommands from the controller 30 and to deposit the fusing agent 26according to a pattern of a cross-section for the layer of the 3D partto be formed. As used herein, the cross-section of the layer of the 3Dpart to be formed refers to the cross-section that is parallel to thesurface of the build area platform 12. In the example shown in FIG. 2C,the applicator 24 selectively applies the fusing agent 26 on thoseportion(s) 40 of the layer 38 that are to be fused to become the firstlayer of the 3D part. As an example, if the 3D part that is to be formedis to be shaped like a cube or cylinder, the fusing agent 26 will bedeposited in a square pattern or a circular pattern (from a top view),respectively, on at least a portion of the layer 38 of the polymeric orpolymeric composite build material particles 16. In the example shown inFIG. 2C, the fusing agent 26 is deposited in a square pattern on theportion 40 of the layer 38 and not on the portions 42.

As mentioned above, the fusing agent 26 may include the metalbis(dithiolene) complex and the FA vehicle. In an example, the fusingagent 26 includes the metal bis(dithiolene) complex, the thiolsurfactant, the polar aprotic solvent, and a balance of water. Inanother example, the fusing agent 26 consists of these components and noother components. In still another example, the fusing agent 26 includesfrom about 1 wt % to about 3 wt % of the metal bis(dithiolene) complex,from about 1 wt % to about 5 wt % of the thiol surfactant, from about 5wt % to about 50 wt % of the polar aprotic solvent, and a balance ofwater (based on the total wt % of the fusing agent 26). As alsomentioned above, in some examples, the fusing agent 26 includes thecolorant. In an example, the fusing agent 26 consists of the metalbis(dithiolene) complex, the thiol surfactant, the polar aproticsolvent, the colorant, and a balance of water. In still other examples,the fusing agent 26 excludes the colorant.

The volume of the fusing agent 26 that is applied per unit of thepolymeric or polymeric composite build material 16 in the patternedportion 40 may be sufficient to absorb and convert enoughelectromagnetic radiation so that the polymeric or polymeric compositebuild material 16 in the patterned portion 40 will fuse. The volume ofthe fusing agent 26 that is applied per unit of the polymer or polymericcomposite build material 16 may depend, at least in part, on the metalbis(dithiolene) complex used, the metal bis(dithiolene) complex loadingin the fusing agent 26, and the polymeric or polymeric composite buildmaterial 16 used.

As shown between FIGS. 2C and 2D, after applying the fusing agent 26,the entire layer 38 of the polymeric or polymeric composite buildmaterial 16 is exposed to electromagnetic radiation (shown as EMRExposure between FIGS. 2C and 2D).

The electromagnetic radiation is emitted from the source ofelectromagnetic radiation 34, 34′ (shown in FIG. 1). The length of timethe electromagnetic radiation is applied for, or energy exposure time,may be dependent, for example, on one or more of: characteristics of theelectromagnetic radiation 34, 34′; characteristics of the polymeric orpolymeric composite build material particles 16; and/or characteristicsof the fusing agent 26.

The fusing agent 26 enhances the absorption of the radiation, convertsthe absorbed radiation to thermal energy, and promotes the transfer ofthe thermal heat to the polymeric or polymeric composite build materialparticles 16 in contact therewith. In an example, the fusing agent 26sufficiently elevates the temperature of the polymeric or polymericcomposite build material particles 16 in layer 38 above the melting orsoftening point of the particles 16, allowing fusing (e.g., sintering,binding, curing, etc.) of the polymeric or polymeric composite buildmaterial particles 16 to take place. Exposure to electromagneticradiation forms the fused layer 44, as shown in FIG. 4D.

It is to be understood that portions 42 of the polymeric or polymericcomposite build material 16 that do not have the fusing agent 26 appliedthereto may not absorb enough radiation to fuse. As such, these portions42 may not become part of the 3D part that is ultimately formed. Thepolymeric or polymeric composite build material 16 in portions 42 may bereclaimed to be reused as build material in the printing of another 3Dpart.

The processes shown in FIGS. 2A through 2D may be repeated toiteratively build up several fused layers and to form the 3D printedpart. FIG. 20 illustrates the initial formation of a second layer ofpolymeric or polymeric composite build material particles 16 on thepreviously formed layer 44. In FIG. 2D, following the fusing of thepredetermined portion(s) 40 of the layer 38 of polymeric or polymericcomposite build material 16, the controller 30 may execute instructionsto cause the build area platform 12 to be moved a relatively smalldistance in the direction denoted by the arrow 20. In other words, thebuild area platform 12 may be lowered to enable the next layer ofpolymeric or polymeric composite build material particles 16 to beformed. For example, the build material platform 12 may be lowered adistance that is equivalent to the height of the layer 38. In addition,following the lowering of the build area platform 12, the controller 30may control the build material supply 14 to supply additional polymericor polymeric composite build material particles 16 (e.g., throughoperation of an elevator, an auger, or the like) and the build materialdistributor 18 to form another layer of polymeric or polymeric compositebuild material particles 16 on top of the previously formed layer withthe additional polymeric or polymeric composite build material 16. Thenewly formed layer may be in some instances preheated, patterned withthe fusing agent 26, and then exposed to radiation from the source ofelectromagnetic radiation 34, 34′ to form the additional fused layer.

Since the metal bis(dithiolene) complex is further reduced and becomescolorless at least during fusing, the layer 44 (and the final 3D part)exhibits a color of the build material (e.g., white or off-white) orexhibits a color of a colorant present in the fusing agent 26. In thelatter example, if it is desirable to impart color to the layer 44, thecolored ink may be selectively applied to at least a portion of thelayer 44.

To further illustrate the present disclosure, examples are given herein.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

EXAMPLES Example 1

An example of the metal bis(dithiolene) complex was prepared in anexample of the polar aprotic solvent and an example of the thiolsurfactant (referred to as “composition 1”). The metal bis(dithiolene)complex used was nickel dithiolene. The polar aprotic solvent used was1-methyl-2-pyrrolidone (1M2P), and the thiol surfactant used wasdodecanethiol, The general formulation of the composition is shown inTable 1, with the wt % of each component that was used.

TABLE 1 Composition 1 Ingredient Special component (wt %) Polar aproticsolvent 1-methyl-2-pyrrolidone 83 Thiol surfactant Dodecanethiol 15 (inwater) Metal bis(dithiolene) Nickel dithiolene 2 complex

The nickel dithiolene, in the presence of dodecanethiol, was readilyreduced and dissolved in the 1-methyl-2-pyrrolidone within seconds atroom temperature. The nickel dithiolene changed colors from green(before reduction) to reddish brown (after reduction).

Composition 1 was incorporated into a vehicle to form a fusing agent.The general formulation of the vehicle is shown in Table 2, with the wt% of each component that was used.

TABLE 2 Ingredient Specific component Vehicle (wt %) Co-solvent1-methyl-2-pyrrolidone 40 Emulsifier CRODAFOS ® O3A 1 Surface tensionSURFYNOL ® SEF 1.5 reduction agent Wetting agent CAPSTONE ® FS-35 0.10Scale inhibitor/Anti- DOWFAX ™ 2A1 020 deceleration agent Chelatingagent TRILON ® M 0.08 Biocide PROXEL ® GXL 0.36 DI (deionized) WaterBalance

The fusing agent included about 50% of composition 1, about 40% of thevehicle, and about 10% of additional deionized water (in addition to thewater already present in the vehicle).

An additional composition (referred to as “composition 2”) containing anexample of the metal bis(dithiolene) complex was prepared in acomparative solvent, namely chloroform. The metal bis(dithiolene)complex used in composition 2 was nickel dithiolene. However,composition 2 did not include the thiol surfactant. The generalformulation of composition 2 is shown in Table 3, with the wt % of eachcomponent that was used.

TABLE 3 Composition 2 Ingredient Specific component (wt %) SolventChloroform 98 Metal bis(dithiolene) Nickel dithiolene 2 complex

Composition 2 was heated to 70° C. for 24 hours to reduce and dissolvethe nickel dithiolene in the chloroform. Composition 2 was incorporatedinto the vehicle shown in Table 2 to form a comparative fusing agent.The comparative fusing agent included about 50% of composition 2, about40% of the vehicle, and about 10% of additional deionized water (inaddition to the water already present in the vehicle).

Composition 1 was also incorporated into the vehicle shown in Table 2 toform a second fusing agent. Composition 1, the vehicle, and theadditional water were used in amounts that provided the second fusingagent with 0.005 wt. % of the nickel dithiolene.

The absorbance of each of the first and second fusing agents and thecomparative fusing agent was measured. The results of the absorbancemeasurements are shown in FIG. 3. The absorbance values are shown alongthe Y axis and the wavelength values in nm are shown along the X axis.As shown in FIG. 3, the maximum absorbance of the first fusing agentshifted to about 940 nm, while the maximum absorbance of the comparativefusing agent was at about 850 nm. The example fusing agent (includingthe polar aprotic solvent, the thiol surfactant, and the metaldithiolene complex) had about a 90 nm shift in the absorbance maximum.

The absorbance of the second fusing agent illustrates that at lowconcentration (e.g., 0.005%), the dye completely reduces to thecolorless state after 24 hours in a reducing solvent. This exampledemonstrates how the dye turns colorless.

Example 2

Several example 3D parts were printed. The build material used to printthe example parts was polyamide-12 (PA-12). The fusing agent used toprint the example parts was the first fusing agent from Example 1 (whichcontained nickel dithiolene, dodecanethiol, and 1-methyl-2-pyrrolidone(1M2P), as well as the vehicle and additional Dl water).

For each example part, the first fusing agent was thermal inkjet printedwith a HP761 printhead (manufactured by Hewlett-Packard Company) in apattern on a portion of the PA-12 in subsequent layers. Each layer wasabout 100 μm in thickness. New layers were spread onto the fabricationbed from a supply region using a roller. The temperature of the supplyregion was set at 115° C. The temperature of the printing region was setat 155° C. with a platen underneath it heated to 148° C. The exampleparts were printed at a contone level ranging from about 20 contone toabout 128 contone (which refers to the number of drops, which is dividedby 256, that will be placed on average onto each pixel). The exampleparts were then exposed to high-intensity light from a halogen lamp witha power ranging from about 500 watts to 750 watts and a colortemperature ranging from about 2700 K to about 3400 K passing over thefabrication bed with a fusing speed ranging from about 20 inches persecond (ips) to about 30 ips. After fusing, the nickel dithiolene wasfurther reduced from its reddish brown form to its colorless form. Afterall layers were printed, the example parts were removed from thefabrication bed and sandblasted to remove excess powder. The exampleparts were not subjected to any further post treatment.

FIGS. 4A and 4B show the example parts in black and white. The exampleparts as formed had vivid colors. FIG. 4A shows a child teeth model inblack and white, and the original photographs showed bright white teethand red gums. The teeth were sharp and strong. FIG. 4B shows four dogbones. From top to bottom, the dog bones (shown herein black and white)were bright pink, bright white, blue, and yellow. The dog bones had atensile strength of about 40 MPa.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 1 wt % to about 3 wt % should be interpretedto include not only the explicitly recited limits of from about 1 wt %to about 3 wt %, but also to include individual values, such as 1.35 wt%, 1.55 wt %, 2.5 wt %, 2.85 wt %, etc., and sub-ranges, such as fromabout 1.35 wt % to about 2.5 wt %, from about 1.5 wt % to about 2.7 wt%, etc. Furthermore, when “about” is utilized to describe a value, thisis meant to encompass minor variations (up to +/−10%) from the statedvalue.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. A fusing agent, comprising: a metalbis(dithiolene) complex; a thiol surfactant; a polar aprotic solvent;and a balance of water.
 2. The fusing agent as defined in claim 1wherein the metal bis(dithiolene) complex has a general formula I

wherein: M is a metal selected from the group consisting of nickel,zinc, platinum, palladium, and molybdenum; and each of W, X, Y, and Z isselected from the group consisting of H, Ph, PhR, and SR, wherein Ph isa phenyl group and R is selected from the group consisting ofC_(n)H_(2n+1), OC_(n)H_(2n+1), and N(CH₃)₂, wherein 2≤n≤12.
 3. Thefusing agent as defined in claim 1 wherein: the polar aprotic solvent isselected from the group consisting of 1-methyl-2-pyrrolidone,2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide(DMF), dimethyl sulfoxide (DMSO), and a combination thereof; and thethiol surfactant is dodecanethiol.
 4. The fusing agent as defined inclaim 1, further comprising a colorant.
 5. The fusing agent as definedin claim 1, further comprising an additive selected from the groupconsisting of a water soluble organic solvent, an emulsifier, a surfacetension reduction agent, a wetting agent, a scale inhibitor, ananti-deceleration agent, a chelating agent, an antimicrobial agent, anda combination thereof.
 6. The fusing agent as defined in claim 1wherein: the metal bis(dithiolene) complex is present in an amountranging from about 1 wt % to about 3 wt % based on a total wt % of thefusing agent; the thiol surfactant is present in an amount ranging fromabout 1 wt % to about 5 wt % based on the total wt % of the fusingagent; and the polar aprotic solvent is present in an amount rangingfrom about 5 wt % to about 50 wt % based on the total wt % of the fusingagent.
 7. A method for making a fusing agent, comprising: exposing ametal bis(dithiolene) complex to a solution including a reducing agentand a thiol surfactant, thereby forming a reduced metal bis(dithiolene)complex and dissolving the reduced metal bis(dithiolene) complex in thesolution; and incorporating the solution into a vehicle including awater soluble organic solvent and an additive selected from the groupconsisting of an emulsifier, a surface tension reduction agent, awetting agent, a scale inhibitor, an anti-deceleration agent, achelating agent, an antimicrobial agent, and a combination thereof. 8.The method as defined in claim 7 wherein the exposing is accomplished ata temperature ranging from about 18° C. to about 25° C.
 9. The method asdefined in claim 7 wherein the reducing agent and the water solubleorganic solvent are the same type of polar aprotic solvent.
 10. Themethod as defined in claim 9 wherein the polar aprotic solvent isselected from the group consisting of 1-methyl-2-pyrrolidone,2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide(DMF), dimethyl sulfoxide (DMSO), and a combination thereof.
 11. Themethod as defined in claim 7 wherein the metal bis(dithiolene) complexhas a general formula I:

wherein: M is a metal selected from the group consisting of nickel,zinc, platinum, palladium, and molybdenum; and each of W, X, Y, and Z isselected from the group consisting of H, Ph, PhR, and SR, wherein Ph isa phenyl group and R is selected from the group consisting ofC_(n)H_(2n+1), OC_(n)H_(2n+1), and N(CH₃)₂, wherein 2≤n≤12.
 12. Themethod as defined in claim 7 wherein the thiol surfactant is selectedfrom the group consisting of dodecanethiol, 1-undecanethiol,2-ethylhexanethiol, 1-octanethiol, 1-tetradecanethiol, and combinationsthereof.
 13. A three-dimensional (3D) printing system, comprising: asupply of polymeric or polymeric composite build material; a buildmaterial distributor; a supply of a fusing agent, the fusing agentincluding: a metal bis(dithiolene) complex; a thiol surfactant; a polaraprotic solvent; and a balance of water; an applicator for selectivelydispensing the fusing agent; a source of electromagnetic radiation; acontroller; and a non-transitory computer readable medium having storedthereon computer executable instructions to cause the controller to:utilize the build material distributor to dispense the polymeric orpolymeric composite build material; utilize the applicator toselectively dispense the fusing agent on a portion of the polymeric orpolymeric composite build material; and utilize the source ofelectromagnetic radiation to expose the polymeric or polymeric compositebuild material to electromagnetic radiation, thereby fusing the portionof the polymeric or polymeric composite build material in contact withthe fusing agent to form a layer.
 14. The system as defined in claim 13wherein the metal bis(dithiolene) complex has a general formula I

wherein: M is a metal selected from the group consisting of nickel,zinc, platinum, palladium, and molybdenum; and each of W, X, Y, and Z isselected from the group consisting of H, Ph, PhR, and SR, wherein Ph isa phenyl group and R is selected from the group consisting ofC_(n)H_(2n+1), OC_(n)H_(2n+1), and N(CH₃)₂, wherein 2≤n≤12.
 15. Thesystem as defined in claim 13 wherein: the polar aprotic solvent isselected from the group consisting of 1-methyl-2-pyrrolidone,2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide(DMF), dimethyl sulfoxide (DMSO), and a combination thereof; and thethiol surfactant is selected from the group consisting of dodecanethiol,I-undecanethiol, 2-ethylhexanethiol, 1-octanethiol, 1-tetradecanethiol,and combinations thereof.